Optical communication systems are widely used today for data communication. Such systems typically use optical fibers as the transmission medium to allow high data rates and long distance transmissions. These optical communication systems commonly utilize optical dense wavelength division multiplexing (DWDM) to exploit the available optical spectrum. In optical DWDM, data is modulated onto several different carrier waves of different wavelengths, with carriers at different wavelengths commonly referred to as channels or channel wavelengths.
In such optical communication systems, the use of pilot tones for identifying the wavelength of an optical data signal is known. The pilot tone will generally be a low frequency modulation (e.g., kHz to MHz) of an optical data signal for channel identification. Each channel wavelength may have a unique pilot tone frequency. Additionally, pilot tones can be modulated themselves, e.g., they can be turned on and off at a low rate, for example, 100 bits/s, to carry additional information, such as the modulation format of the optical data signal, the origin of the optical data signal, the optical spectrum width, baud rate, etc. Pilot tone detectors (PTDs), which may consist of a low speed photodiode and a digital signal processor (DSP), may be placed at many locations in an optical network to monitor channel information, such as wavelength or other information carried on pilot tones, providing a low cost, efficient solution for managing optical DWDM systems.
However, the inclusion of a pilot tone as a modulation of an optical data signal can reduce the optical signal to noise ratio (OSNR) of the optical data signal.
Improvements in optical receivers to compensate for the pilot tone induced OSNR penalty are therefore desirable.